"However, ProRes is really just an imitation of Avid's DNx platform..."
ProRes - 2007
DNXHD - 2008
Use what you want, but a $40 dongle isn't enough to make me want to change workflows, fight with drivers, viruses, etc.
Panasonic is always loath to comment on DR. Several video reviews from early users state 14 stops, but that seems unlikely. Others have said "improved highlight roll-off" which seems more likely.
The GH5 is the camera for you. Panny had to make some trade-offs. By jettisoning IBIS the GH5s can work in scenarios the GH5 cannot.
No. There is no "off" in the sense that the sensor is always floating on springs with magnets holding it "off." IBIS sensors can't be physically locked in place.
Not saying I'm not disappointed, too, but the logic is sound. IBIS sensors can't ever really be "off" and lock in place...the magnets simply hold them steady. There are situations where this can fail (car mounting is one such scenario.) The other factor is heat dissipation. A floating sensor can't void heat the way a fixed sensor can, and if you want to attack sensor noise, dealing with heat is one of the keys.